For quite a long while I've had mint 9 &10 on my laptop and today switched to a Mint 12 KDE/Win 7 dual boot. Everything went fine but when I try to update I get two or three errors. Whats strange is that they're not always the same and some are pretty weird. The most common one though is that said repo is unfound - a 404 error. And also I get this error from synaptic when I try to refresh.

I've been using Mint for a number of years but I've never had reason to mess around with the sources list so while I have added plenty of repos myself I've never opened up my sources list. Given that fact I'm at aa loss to see the problem. Any help would be great. Thanks.